Align data collators across DPO / SFT / Reward / KTO

[qgallouedec]

Consistency pass over the data collators so the same thing is written the same way everywhere. No behavior change.

• Docstrings: unified intro lines, arg wording (max_length, truncation_mode, return_tensors) and the # special case for Qwen2.5-VL comment. Added the missing Examples blocks to the KTO collators.
• Naming: KTO batch → output, ex → example, torch.int64 → torch.long.
• Structure: KTO vision now uses inline "token_type_ids" in processed_prompts checks (dropping the has_tti/has_mm_tti locals) so its flush-left / truncate / output blocks match DPO/SFT word-for-word; simplified mm_token_type_ids handling to match.
• Fixed a misplaced comma in the repeated BOS comment.

Deeper output-key naming/semantics (e.g. KTO's completion_input_ids holds prompt+completion) is left for a follow-up PR.

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Note

Low Risk
Collator-only refactor with stated no behavior change; the mm_token_type_ids merge simplification could affect edge-case VLMs if completion tensors previously carried non-zero mm types.

Overview
Consistency pass across DPO, SFT, and KTO data collators so docstrings, naming, and vision collator control flow match; the PR description states no intended behavior change.

Documentation: Unified max_length, truncation_mode, and return_tensors wording; expanded KTO text and vision collator docs with Examples blocks; reordered DPO vision output key list; clarified SFT max_length as truncate-before-pad for text collators.

KTO text collator: Renames batch → output, ex → example; uses torch.long instead of explicit int64 on tensors; adds inline Truncate / Pad comments aligned with DPO.

Vision collators (KTO, DPO, SFT): Replaces has_tti / has_mm_tti locals with inline "token_type_ids" in processed_prompts checks; aligns flush-left, truncate, and output blocks with DPO/SFT; sets completion-side mm_token_type_ids via torch.zeros_like(completion_ids) instead of merging processor completion mm_token_type_ids (KTO KL path similarly); fixes BOS comment typo (BOS, twice → BOS twice); DPO adds a Truncate if necessary comment before the vision truncation block.

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